Contaminating ion removal



Nov. 4, 1958 a E. F.-FREKKO 2,859,161

CONTAMINATING ION REMOVAL Filed June 13, 1957 I .L 10 I 5 55 12 I I p INV E NTOR EUGENE E FREKKO ATTORNEY United States Patent CONTAMINATING ION REMOVAL Eugene F. Frekko, Sanford, N. C., assignor to Cornell- Dubilier Electric Corporation, South Plainfield, N. 1., a corporation of Delaware Application June 13, 1951, Serial No. 665,438 2 Claims. (Cl. 204-130 This invention relates to a method and apparatus for simply and economically effecting removal of minute quantities of ionizable contaminating materials from solutions and is a continuation-in-part of my United States patent application Serial No. 533,738, filed September 12, 1955, now abandoned.

The removal of minute quantities of'contaminating impurities from solutions is frequently a commercial or laboratory necessity. This is particularly true in the case of undesired contaminants in the form of ionizable materials in a solution. Extremely small quantities, oftentimes in the order of only a few parts per million, of a contaminating ion may be highly objectionable and require time consuming and expensive operations to effect the removal thereof.

It is the object of this invention to provide a means and method for simply and economically efiecting'the removal of contaminating ionized impurities from solu tions containing undesired minute quantities thereof.

Referring to the drawings:

Fig. 1 shows a side diagrammatic view of one embodiment of this invention; and

Fig. 2 shows a side diagrammatic view of the modification of this invention.

Its general aspects, the subject matter herein presented provides a simple and inexpensive apparatus and a simple and easily practiced method by which ions of a contaminating impurity in a liquid can be selectively and continuously removed therefrom on a moving electrode which is subsequently treated to remove the contaminating impurity therefrom. In a preferred embodiment a movable electrode, in the form of an endless strip of a suitable metal, for example aluminum or titanium, is so arranged as to be continuously displaced through a bath containing the solution having the contaminating impurity therein to remove the contaminating impurity therefrom followed by sequential displacement of the electrode through other baths to remove the adherent contaminating impurities from the electrode element.

Referring to Fig. 1, there are provided three tanks 10, 11 and 12. The tanks each contain a bath identified by the reference numerals 13, 14, and 15 respectively. A conductive strip 16, preferably formed of aluminum or titanium, is arranged to be displaced sequentially through the tanks 10, 11 and 12 by means of freely rotating rollers 17 through 21. As shown in Fig. l, the preferred embodiment is in the form of an endless strip which, by means of auxiliary roller 22 and drive roller 23 is arranged to travel in a closed circuit through V the baths 13, 14 and 15. The conductive strip 16 is arranged to be electrically charged, as by a contacting charging roller 24 connected to a suitable source of potential of one polarity such as the positive terminal of a generator and to thereby serve as a continuously moving electrode element.

The tank is preferably connected to a source of potential of opposite polarity from that connected to the strip-16, conveniently the negative terminal of the I minute amounts in solutions.

2,859,161 Patented Nov. 4, 1 958 above mentioned generator, thereby creating a potential difference between the tank and the strip, the magnitude of which is determined by the actual potentials employed. For removal operations wherein the tank 10 serves as a cathode the tank is formed of a suitable metal such as stainless steel and is provided with an insulated jacket 25a.

The tank 11 is electrically isolated relative to the remainder of the system. This may be effected by surrounding the tank with a coating of suitable insulating material 25b. In the embodiment illustrated in Fig. 1, the tank 12, surrounded by an insulating jacket 250, is connected to a potential of opposite polarity as that applied to the tank 10, conveniently the positive terminal of another generator with the strip .16 being connected to the negative terminal thereof, thereby creating a potential difference intermediate the strip 16 and tank 12 opposite to that extant between thestn'p 16 and tank 10. With such a connection the tank 12 serves as an anode and should be preferably formed of graphite or other non-metallic conductive material.

The tank 10 is adapted to contain a bath 13 of the contaminated solution. The intermediate tank 11 is adapted to contain a bath 14. of a suitable solvent for the contaminating impurities present in bath 13. The bath 15 in tank 12 is adapted to contain a suitable electrolyte to permit further removal of the contaminating impurities from the strip 16 as it passes therethrough.

In operation of the unit, the solution containing the ionized contaminating impurity is placed in tank 10. The solvent employed may be Water, ethylene glycol, glycerine, alcohol or similar well known solvents. The solution is made weakly electrolytic by the use of a weak electrolyte such as boric or citric acid or similar weak electrolytes. A solvent for a salt formed of the contaminating ion and the belt material is placed in tank 11. In view of the extremely small quantities of contaminating impurities involved, utilization of the same solvent as employed in bath 13 may be almost universally effected. The bath 15 in tank 12 is preferably formed of the same solvent employed in tank 10 and the solution is made weakly electrolytic by the addition of a quantity of a weak electrolyte, preferably the same as heretofore employed. The belt or strip 16 is then threaded around the guide rollers as indicated in the drawing. In the instance where the contaminating ion desired to be removed is an anion, the strip 16 is positively charged relative to the tank 10 and the tank 12 is positively charged relative to the strip 16. The strip is then set in motion in a direction so as to first pass through the bath 13 in tank 10, thence through bath 14 in tank 11, thence through bath 15 in tank 12 and then, after a relatively extended length of return path, to repeat the above cycle.

The invention herein described has been found to be extremely useful in eifecting the simple and expeditious removal of ionized contaminating impurities present in It has been found particularly efficacious in effecting the removal of contaminant chloride ions when present in minute quantities, say about 5 parts per million. For example, a suitable bath 13 may be made up of 111 grams of ethylene glycol or other polyalcohol as a solvent, 5 to 15 grams of boric acid and .08 to .2% of sodium or ammonium borate. This bath should also contain a small percentage of ionizable contaminant such as about 5 parts per million of sodium chlo ride. The bath 14'should contain ethylene glycol and the bath 15 in tank 12 also contains ethylene glycol with 5 to 10% boric acid added thereto to form a weak electrolytic'solution.

' A potential ditference of about volts is then applied between strip 16 and tank 10, a potential difference of about volts is applied between tank '12 and the strip 16, and the strip 16 is set in motion at a rate of about 12 inches per minute.

Under the above conditions displacement of the strip 16 will effect a reduction of the concentration of'the contaminating sodium chloride from about 51parts per illion to about .5 part per million in about 2"hou r s' qr less.

Equally efficacious results can be obtained with the use of water instead of ethylene glycol as a solvent in the baths 13, 14 and 15 and by the use ,of citric acid and sodium or ammonium citrate instead of the 'boric acid and borates set forth above.

The mechanics of the operations that actually effect the removal of the contaminating ions are not completely understood at the present time but it is applicants present belief and theory that operations and actions essentially of the following nature take place.

In the above example where the contaminating impurity is in the form of a chloride ion (C-l), the application of a positive potential to the strip 16 and a negative potential to the tank 10 causes the strip 16 to act as a positive electrode. As the strip 16 is more electroposie tive than the tank 10, a potential difference is created of sufficient magnitude to cause the chloride ions or anions to migrate through the bath 13 toward the strip 16. The migration of the chloride anions toward and to the strip 16 results in a relatively high concentration of chloride ions in the immediate vicinity of the strip 16. It is thought that the concentration of chloride ions in the vicinity of the strip may result in a reaction or combination by a certain amount thereof with the elemental aluminum at the strip surface to form aluminum chloride which is then hydrolized to release the chlorine ions.

Fluid film theory indicates that the film of solution immediately adjacent the moving strip is displaced in accordance therewith. As such the displacement of the strip 16 through the bath 13 and its subsequent removal therferom also effects removal of the adjacent layers-of solution. Consequently since the chloride ion concentration should be the greatest in these layers, removal of the strip from the bath results in removal of chloride ions in the liquid film adherent thereto. However, whether or not the above theoretical assertions as to the possible action truly characterize the operations performed, the fact remains that passage of the strip 16 through the bath 13, as described above, effects a marked reduction in the chloride ion concentration therein.

The strip 16 is then introduced into the bath 14 in tank 11. As indicated earlier the tank 11 is electrically thereof are essentially non-electrolytic in nature and of through the electrolytic bath 15, the reversed potential gradient makes the strip 16 act as a negative electrode and causes the remainder of the aluminum chloride to go into solution, become ionized and causes the chloride ions to migrate away from the strip 16 and toward the tank 12 which is now functioning as an anode and which, as indicated earlier, is preferablyformed of graphite. By

this further treatment, all, or practically all, of the remaining contaminating ions associated with the strip 16 are emo e th r from- In certain installations, it.may be inconvenient or impractical to employ a third tank of graphite or other suitable material. In such instances the application of potential to the third tank maybe dispensed with and a further treatment by purely mechanicalmeans may be employed. Such mechanical treatment may not be as completely effective as the treatment heretofore described with the result that, with all other factors being equal, it may take slightly longer to effect a desired degree of removal Of contaminating impurities. However, such increased time may more than offset, in certain installations, the inconvenience or impracticality of using the means and method heretofore described. A suitable unit for further treatment of a mechanical nature is illustrated in the modification of this invention as shown in Fig. v2. The apparatus there illustrated may be identical with that shown and described heretofore in connection with Fig. 1,

except that the tank 12 is not connected to a source of electrical potential but preferably is electrically isolated in a manner similar to that described earlier in conjunction with tank 11. The passage of the strip through tank 12 effects a further removal of contaminant by dilution or simple solution similar to that described earlier from impinges on the strip 16 and effects a further mesuch character as to be solvent. The lack of any potential gradient between the bath 14 and the strip 16 reduces any tendency of the contaminant ions on the strip to adhere thereto or to further migrate theretowards. The immersion of the strip 16 in the bath 14 thus serves to wash off and/ or otherwise dilute the liquid film adhering to the strip. The result of passing the strip 16 through the bath 14 is the effective removal ofa substantial if not the greater portion of the contaminating impurities'carried by the strip by dilution and/ or simple solution. However, immersion intank 11 will not removeallof the chloride ions associated with the. strip 16 in tank 10 Iand a further treatment is preferable in order to. further .clean the strip 16 prior to its reentry into tank 10.

The embodiment illustrated in Fig. 1 shows one method for such further treatment. As there shown, the strip 16, in its normal progression, is then displaced out of the tank 11, over the roller 20 and introduced downwardly into the tank 12 to pass under theroller 21 disposed therein. As pointed out above, the tank 12 is maintained electropositive in respect to strip1 6by connecting the tank 12, in the illustrated example, to a positivepotentialand thestrip 16 to a negative potential. As the strip 16 passes chanical removal of any of the contaminating ions still adher t h r n- I 'The actual potentials employed in conjunction with the described apparatus may be varied over a wide range as long as the proper direction of potential differences are maintained. Potential differences in the order of 6 volts have been found to be operative although potential differences in the order of volts are preferred for efficient and relatively rapid operation. Although the apparatus efficiently operates in the removal of chloride ions as heretofore indicated and explained the described process will also effectively remove sulphate, nitrate and other negative ions.

The apparatus and process of this'in'vention have been employed to provide a purification by the removal of ionized impurities from an original concentration in the order of 5 parts per million to a purified solution of Other advantages of this invention are the simplicity and economy of the.

the order of .5 part per million.

construction and its flexibility and adaptability in operation. The same equipment may be used to purify a variety of solutions by the removal of a number of contaminating ions.

I claim:

1. A method of removing undesired ionizable chloride said first bath and passing the same through an electrically isolated second bath containing a solvent solution for said chloride impurities to reduce the concentration of said ionized impurities adjacent thereto.

2. A method of removing undesired ionizable chloride impurities as set forth in claim 1 including the steps of removing said electrode from said second bath and passing the same through a third bath containing a solvent solution rendered Weakly electrolytic by the addition of boric acid thereto and applying a potential difierence between said electrode and third bath of a polarity References Cited in the file of this patent UNITED STATES PATENTS Domm Aug. 25, 1942 Tainton Feb. 16, 1943 

1. A METHOD OF REMOVING UNDESIRED IONIZABLE CGLORIDE IMPURITIES FROM A SOLVENT SOLUTION OF ETHYLENE GLYCOL CONTAINING SMALL CONCENTRATION OF THE SAME COMPRISING THE STEPS OF PROVIDING A FIRST BATH OF SAID CONTAMINATED SOLVENT SOLUTION RENDERED WEAKLY ELECTROPLYTIC BY THE ADDITION OF BORIC ACID THERETO, INTORDUCING INTO SAID BATH A PORTION OF A CONTINUOUSLY MOVING ENDLESS ALUMINUM BELT ELECTRODE ELEMENT, APPLYING A POTENTIAL DIFFERENCE INTERMEDIATE SAID ELECTRODE AND BATH OF A POLARITY TO ATTRACT IONS OF SAID CHLORIDE IMPURITY TO SAID MOVING ELECTRODE AND TO CONCENTRATE THE SAME IMMEDIATELY ADJACENT THERETO, AND REMOVING SAID ELECTRODE PORTION AND IMPURITY CONCENTRATED LIQUID FILM ADHERENT PORTION AND SAID FIRST BATH AND PASSING THE SAME THROUGH AN ELECTRICALLY ISOLATED SECOND BATH CONTAINING A SOLVENT SOLUTION FOR SAID CHLORIDE IMPURITIES TO REDUCE THE CONCENTRATION OF SAID IONIZED IMPURITIES ADJACENT THERETO. 